A production process for beer, low-malt beer, distilled liquor, etc., includes a roasting-and-drying process for drying and roasting green malt provided by germinating barley. The roasting-and-drying process stops the growth and the lytic reaction of green malt that is a raw material by drying the green malt, so as to prevent the putrefaction and the spoilage and to allow the storage of the green malt. Additionally, it is performed in order to eliminate natural odor of green malt and to produce a dye and a flavor.
The roasting and the drying are performed for a short time period such as 1–2 days and nights so as to provide physical and chemical changes that determine the quality and the kind of malt and are the last processes in a malt production process, so that the process control is important for beer production that aims at obtaining a high quality beer. In particular, in the roasting-and-drying process, the drying temperature and speed and the roasting temperature have impacts.
As a roasting-and-drying method, provided are direct-firing roasting-and-drying methods of passing a combustion gas directly through a malt layer in a roasting-and-drying room and indirect hot-air roasting-and-drying methods with indirect heated air. Among the indirect heating methods, one popular method is performed so that air is heated by a heat exchanger and is blown into a green malt layer by an air blower. The air is taken in from outside air and the amount of air necessary to dry a given amount of green malt varies depending on the temperature and the humidity of the air.
The green malt layer, which normally has a height of 0.8 through 1.2 m for a one-floor method or 20 cm–30 cm for a two-floors or three-floors method, is uniformly distributed on a floor, and roasting and drying are controlled by the air blower while a ventilating valve (damper) is controlled to be open or closed.
In a drying process in the roasting-and-drying process, factors such as the temperature, the time period, and further the blown air amount have impacts, as is described above, and, particularly, in large-scale drying equipment, the humidity of outside air has an impact. Of course, the humidity of the outside air varies dependent on weather, and the reason why the degree of the drying varies dependent on weather is that the absolute humidity of the air (that is, the amount of moisture contained in the air; g/L) varies.
Conventionally, in the drying process, the controlling of the temperature, the drying time period, the blown air amount, etc., has been performed so as to accomplish roasting and drying with a constant quality. The controls of the processes have been performed by way of adjusting the taken-in amount of outside air, etc., based on room temperature, room relative humidity, or the relative humidity of the outside air, depending on experience, but the appropriate controls of heating temperature, the blown air amount, etc., have not been based on the absolute humidity of the outside air, and thus there is a need for a drying method capable of finer control and being able to achieve desired roasting and drying.
In the present invention, when heated air is fed to a malt layer in a roasting-and-drying process, the absolute humidity of outside air is continuously monitored, thereby controlling the blown air amount so as to perform more appropriate drying, based on the knowledge that the influence of the variation of the absolute humidity of the outside air, not the relative humidity thereof, on drying is large.